Anatomy & Function

What is the anal sphincter — and what does it do?

The anal sphincter is a ring of muscle that surrounds the anal canal — the very end of the bowel — and acts as the body's valve for controlling motions. It is what allows you to hold stool and wind, and to choose when to release them. This control, called continence, is something we rarely think about until it is threatened.

There are two muscles working together. The internal anal sphincter is an involuntary muscle that stays closed automatically, keeping the canal sealed at rest. The external anal sphincter is a voluntary muscle you can squeeze consciously to hold on when you feel the urge. Together with the puborectalis muscle of the pelvic floor, they form the continence mechanism.

How it works: when stool arrives in the rectum, the rectum stretches and signals the urge to go. The internal sphincter relaxes to "sample" the contents, while the external sphincter and pelvic floor stay tight, giving you time to reach a toilet. When you are ready, you relax the muscles voluntarily and the rectum empties. This delicate reflex depends on healthy muscle and healthy nerves.

Why it matters: losing the sphincter means losing natural control — stool then has to be diverted to a permanent stoma on the abdomen. Preserving the sphincter preserves dignity, body image and quality of life. This is why saving it, whenever cancer safety allows, is so important.

Two things must survive for continence: muscle and nerves

A sphincter that is anatomically present but has lost its nerve supply will not work properly. That is why sphincter-preserving surgery is about more than keeping the muscle — it also means protecting the fine pelvic autonomic nerves that control the sphincter, the bladder and sexual function. Precise, nerve-sparing dissection (TME) is central to a good outcome.

The Challenge

What puts the sphincter at risk during rectal surgery

Two separate things can threaten continence when operating on rectal cancer — the position of the tumour, and injury to the nerves. Understanding both explains how we protect them.

Margin

When the tumour reaches the sphincter

To cure rectal cancer, the tumour must be removed with a clear margin of healthy tissue all around and below it. If the tumour grows right down to — or into — the sphincter muscle, there may be no safe soft-tissue margin left below it. In that situation, keeping the sphincter would mean leaving cancer behind, which is not acceptable.

Nerves

Damage to the pelvic nerves

The fine autonomic nerves running alongside the rectum control the sphincter, bladder and sexual function. Careless dissection can injure them, leaving the sphincter muscle intact but poorly functioning. Meticulous nerve-sparing TME protects them.

Height

How low the tumour sits

The closer the tumour is to the anal verge, the harder preservation becomes. Distance from the anal verge — measured carefully — is one of the most important factors in deciding what is possible.

Function

Pre-existing weak sphincter

If the sphincter is already weak — from age, childbirth injury or other causes — preserving it may leave a patient with poor control. Honest assessment of baseline function matters as much as the cancer itself.

The Decision

When we preserve — and when we must remove

The goal is always to cure the cancer first, and preserve the sphincter wherever that can be done safely. These are the factors that guide the decision — weighed together, never in isolation.

Criteria for sphincter preservation vs removal
Factor	Favours preserving the sphincter	Favours removing it (permanent stoma / APR)
Tumour height	Sufficient distance from the anal verge / a safe distal margin achievable	Very low tumour at or below the sphincter with no margin
Sphincter involvement	Tumour does not invade the sphincter muscle	Tumour directly invades the sphincter complex
Distal & circumferential margin	Clear soft-tissue margin obtainable below and around the tumour	No clear margin possible without leaving cancer
Response to neoadjuvant therapy	Good shrinkage after chemoradiotherapy, creating a margin	Poor response; tumour still fixed to sphincter
Baseline sphincter tone & continence	Good resting tone and squeeze on examination	Already weak/incontinent — preservation would give poor function
Patient factors & wishes	Fit, motivated, accepts intensive aftercare and possible LARS	Frailty or strong preference for predictable stoma function

The guiding principle: cure is never traded for sphincter preservation. But with modern neoadjuvant treatment and advanced techniques, a safe margin can often be created where it once seemed impossible — so far fewer patients need a permanent stoma than in the past.

Patient Selection

How we assess whether the sphincter can be saved

Choosing the right patients for sphincter preservation is a careful, multi-step assessment. No single test decides it — they are combined.

Examination

Digital rectal examination (DRE)

A careful finger examination by the surgeon assesses how low the tumour is, whether it is mobile or fixed, how close it lies to the sphincter, and — crucially — the resting tone and squeeze strength of the sphincter itself. This hands-on assessment is irreplaceable.

Sphincter tone

Assessing baseline continence

Good sphincter tone is essential — there is little point preserving a sphincter that cannot work. We ask about existing control of stool and wind, and test the squeeze. Where needed, anal manometry can measure sphincter pressures objectively.

Imaging

High-resolution pelvic MRI

MRI is the key scan. It shows the exact height of the tumour, its distance from the sphincter, whether it threatens the circumferential margin, and the involvement of nodes — mapping precisely what surgery can achieve. It is repeated after neoadjuvant treatment to reassess.

Endoscopy

Colonoscopy & biopsy

Confirms the diagnosis, the exact level, and rules out other tumours higher in the bowel.

MDT

Multidisciplinary tumour board

Surgeon, radiation and medical oncologists and radiologist agree the plan together — including whether neoadjuvant therapy should come first to make preservation possible.

Techniques

The ways we preserve the sphincter

Sphincter preservation is not one operation but a strategy — often combining treatment to shrink the tumour first with a precise operation to remove it while saving the muscle.

Rectal Cancer Surgery - Dr. Vinod T. Gore

Step 1 · Shrink

Neoadjuvant radiotherapy / chemoradiotherapy

For low or locally advanced tumours, radiotherapy — usually combined with chemotherapy (chemoradiotherapy) — is given before surgery. It shrinks the tumour and can create a safe margin below it, turning a sphincter-threatening tumour into one that can be removed with the sphincter preserved. Total neoadjuvant therapy (all chemo + radiotherapy first) is used in selected cases for even better downstaging.

Step 2 · Remove (TME)

Total Mesorectal Excision with nerve-sparing

The core cancer operation: the rectum and its surrounding fatty envelope (mesorectum) are removed completely along precise planes, sparing the pelvic autonomic nerves. Good TME gives both the best cure and the best function. Often done robotically for precision deep in the pelvis.

Option · LAR

Low Anterior Resection (LAR)

The rectum containing the tumour is removed and the colon is rejoined to the remaining rectum or anal canal (anastomosis), keeping the sphincter and natural route. Suitable when there is enough healthy rectum/canal below the tumour. A temporary covering ileostomy is usually made to protect the new join while it heals (see below).

Option · ISR

Intersphincteric Resection (ISR)

For very low tumours close to the sphincter, ISR removes the internal sphincter (and the tumour) while preserving the external sphincter, then joins the colon to the anal canal — saving natural control where a permanent stoma once seemed the only option. Demands meticulous technique and careful selection.

Protect

Covering (temporary) ileostomy

After a low join (LAR or ISR), a temporary loop ileostomy diverts stool to let the join heal safely, greatly reducing the risk of a leak. It is planned for reversal — usually after 8–12 weeks (later if chemotherapy is needed). The stoma is temporary; the sphincter is saved.

Neoadjuvant CRT Total neoadjuvant therapy Nerve-sparing TME LAR · colo-anal anastomosis ISR Temporary loop ileostomy Robotic precision

Learn more about stoma care & reversal and robotic rectal surgery.

After Surgery

Aftercare & protecting your function

Saving the sphincter is the beginning; helping it work well afterwards is just as important. With the right aftercare, bowel control improves steadily over the first one to two years.

Pelvic floor

Pelvic floor (sphincter) exercises

Regular pelvic floor exercises strengthen the sphincter and pelvic muscles, improving control after surgery. Often guided by a physiotherapist, they are one of the most effective things you can do — done daily, they make a real difference.

Bowel function

Managing LARS (bowel changes)

After a low join, many people experience Low Anterior Resection Syndrome — frequency, urgency or clustering of motions — which usually improves over 1–2 years. Diet, routine, medication, bowel retraining and pelvic floor work all help, tailored to your pattern.

Diet

Diet & routine

Identifying trigger foods, eating at regular times and keeping a food-and-symptom diary in the early months help settle the bowel into a predictable pattern.

Stoma

Timely ileostomy reversal

If a covering ileostomy was made, it is reversed once the join has healed and any chemotherapy is complete — confirmed by a scan or scope first. Expect frequent, loose motions at first that settle with time and the measures above.

Support

Specialist help for persistent symptoms

For control that remains troublesome, options such as transanal irrigation, biofeedback or nerve stimulation can help. You are reviewed at follow-up and never left to cope alone.

See our dedicated page on Stoma Care & Reversal, which covers LARS and pelvic-floor recovery in detail.

Patient Questions

Sphincter preservation — answered plainly

In the great majority of rectal cancers today, yes — the sphincter can be saved. But it depends on how low the tumour is, whether it involves the sphincter, and how it responds to treatment. Dr. Gore will give you an honest assessment after examination and MRI. Where a permanent stoma truly is the only safe option for cure, that will be explained clearly — but it is needed far less often than in the past.

If the tumour grows into the sphincter muscle or sits so low that no clear margin can be obtained below it, preserving the sphincter would mean leaving cancer behind. Cure must come first. We also consider sphincter strength — preserving a sphincter that cannot work would not help you.

Given before surgery, it shrinks the tumour and can pull it away from the sphincter, creating the clear margin needed to remove the cancer while keeping the muscle. A tumour that looked sphincter-threatening at diagnosis can become preservable after a good response — which is why we reassess with MRI afterwards.

Both save the sphincter. LAR (Low Anterior Resection) removes the rectum and rejoins the colon above the sphincter — used when there is enough healthy canal below the tumour. ISR (Intersphincteric Resection) goes lower, removing the internal sphincter for very low tumours while keeping the external sphincter, then joining the colon to the anal canal. ISR saves natural control in cases that once needed a permanent stoma.

Often yes — a temporary loop ileostomy is usually made to protect the new low join while it heals, which reduces the risk of a leak. It is planned for reversal, typically after 8–12 weeks (later if chemotherapy is needed). It is a temporary step, not a permanent bag — your sphincter is preserved.

At first you may have frequency, urgency or clustering of motions (LARS), which usually improves over 1–2 years as the bowel adapts. Pelvic floor exercises, diet, routine and medication all help a great deal, and we support you throughout. Most people settle into a manageable, predictable pattern.

Very. Regular pelvic floor exercises strengthen the sphincter and pelvic muscles and are one of the most effective ways to improve control after sphincter-preserving surgery. Done daily — ideally guided by a physiotherapist — they genuinely speed and improve recovery.

This page is general information, not personal medical advice. Whether the sphincter can be preserved is an individual decision based on examination, MRI and tumour response, always made with cure as the first priority. Please bring all scans and reports to your consultation.

Silver Leaf Clinic · Hadapsar, Pune

Ask whether your sphincter can be saved

If you have been told you may need a permanent stoma for rectal cancer, a specialist second opinion is worthwhile — modern techniques save the sphincter far more often than before. Please bring your MRI and CT scans, colonoscopy and biopsy reports, and any previous notes — ideally on CD or shared via WhatsApp in advance.

Dr. Gore Direct / WhatsApp

84118 08284

📍 Clinic Address

511, City Centre, Solapur Road, Opp. Vaibhav Theatre, Hadapsar, Pune 411028

📍 Open in Google Maps →

Monday – Saturday10:00 AM – 6:00 PM

SundayBy prior appointment

Surgical Hospital

Sahyadri Manipal Hospital, Pune · Robotic Cancer Surgery Centre of Excellence